1. Field of Invention
The present invention relates to data storage generally and more particularly to holographic data storage.
2. Description of Related Art
A variety of multiplexing methods have been developed to take advantage of the large storage capacity of holographic media including angle multiplexing, peristrophic multiplexing, wavelength multiplexing, phase coded multiplexing, shift multiplexing, and spatial multiplexing. (Holographic Data Storage, H. J. Coufal, D. Psaltis, and G. T. Sincerbox, (eds.), Springer-Verlag 2000.) These methods have also been used in combination to achieve higher performance (e.g, angle and peristrophic multiplexing). In many cases, however, these methods have been developed without a substantial appreciation for the practical requirements associated with the configuration of a manufacturable storage product. Mechanical tolerances corresponding to the system""s requirements for error-free recovery of data are often difficult to achieve or prohibitively expensive for methods that are theoretically feasible.
For example, conventional shift multiplexing and tilt multiplexing (U.S. Pat. No. 5,703,705) were originally conceived as relatively easy-to-implement methods for multiplexing holograms by moving the media. While conceptually simple, practical mechanical implementation of these methods has proved difficult in many operational settings. Access of individual holograms may require movement of a massive object, (e.g., the piece of media) both quickly (e.g., with sub-msec timing) and accurately (e.g., with sub-micron tolerances).
Therefore, there is a need for developing multiplexing methods for holographic storage systems to achieve high storage capacities in simple-to-implement mechanical geometries more consistent with realistic optical storage devices and current limitations for drive designs.
In one embodiment of the present invention, a method of recording holograms includes: generating a first signal beam from a signal-beam source and a first reference beam from a reference-beam source; recording a first hologram in a holographic medium from an interference between the first signal beam and the first reference beam; shifting the reference-beam source after the act of recording the first hologram; generating a second signal beam from the signal-beam source and a second reference beam from the reference-beam source after the act of shifting the reference-beam source following the recording of the first hologram; and recording a second hologram in the holographic medium from an interference between the second signal beam and the second reference beam.
According to one aspect of this embodiment, the method may further include: shifting the holographic medium after the act of recording the second hologram; generating a third signal beam from the signal-beam source and a third reference beam from the reference-beam source after the act of shifting the holographic medium following the recording of the second hologram; and recording a third hologram in a holographic medium from an interference between the third signal beam and the third reference beam. Additionally according to this aspect, the method may include: shifting the reference-beam source after the act of recording the third hologram; generating a fourth signal beam from the signal-beam source and a fourth reference beam from the reference-beam source after the act of shifting the holographic medium following the recording of the third hologram; and recording a fourth hologram in the holographic medium from an interference between the fourth signal beam and the fourth reference beam.
According to another aspect, shifting the reference-beam source may include shifting a reference-beam lens. According to another aspect, shifting the reference-beam source may include adjusting a reference-beam mirror that shifts a spherical origin for reference beams. According to another aspect, shifting the reference-beam source may include shifting for tilt selectivity.
In another embodiment of the present invention, an apparatus for recording holograms includes: a signal-beam source for generating signal beams; a reference-beam source for generating reference beams; a holographic medium for recording holograms; and a reference-beam-source drive for shifting the reference-beam source. An interference between a first signal beam and a first reference beam records a first hologram in the holographic medium.
This embodiment of the present invention may include aspects described above. According to another aspect, the apparatus may include a laser source and a data source for providing inputs to the reference-beam source and the signal-beam source. According to another aspect, the apparatus may include a holographic-medium drive for shifting the holographic medium. According to another aspect, the reference-beam source may include a reference-beam lens. According to another aspect, the reference-beam source may include a reference-beam mirror that shifts a spherical origin for reference beams. According to another aspect, the holographic medium may include reflective media.
In another embodiment of the present invention, a method of reading holograms includes: generating a first reference beam from a reference-beam source; reading a first hologram in a holographic medium from a diffraction of the first reference beam with the first hologram; shifting the reference-beam source after the act of reading the first hologram; generating a second reference beam from the reference-beam source after the act of shifting the reference-beam source following the reading of the first hologram; and reading a second hologram in the holographic medium from a diffraction of the second reference beam with the second hologram.
This embodiment of the present invention may include aspects described above. According to another aspect, the method may further include: shifting the holographic medium after the act of recording the second hologram; generating a third reference beam from the reference-beam source after the act of shifting the reference-beam source following the reading of the second hologram; and reading a third hologram in the holographic medium from a diffraction of the third reference beam with the third hologram. Additionally according to this aspect, the method may include: shifting the reference-beam source after the act of reading the third hologram; generating a fourth reference beam from the reference-beam source after the act of shifting the reference-beam source following the reading of the third hologram; and reading a fourth hologram in the holographic medium from a diffraction of the fourth reference beam with the fourth hologram.
According to another aspect, shifting the reference-beam source may include shifting a reference-beam lens. According to another aspect, shifting the reference-beam source may include adjusting a reference-beam mirror that shifts a spherical origin for reference beams. According to another aspect, reading the holograms may include using an aperture in a reconstruction arm of the holograms. According to another aspect, shifting the reference-beam source may include shifting for tilt selectivity.
In another embodiment of the present invention, an apparatus for reading holograms includes: a holographic medium with holograms recorded therein; a reference-beam source for generating reference beams to read the holograms recorded in the holographic medium; a reference-beam-source drive for shifting the reference-beam source. A diffraction between a first reference beam and a first hologram in the holographic medium generates a first signal beam.
This embodiment of the present invention may include aspects described above. According to another aspect, the apparatus may further include a laser source and a data source for providing inputs to the reference-beam source. According to another aspect, the apparatus may further include a holographic-medium drive for shifting the holographic medium. According to another aspect, the reference-beam source may include a reference-beam lens. According to another aspect, the reference-beam source may include a reference-beam mirror that shifts a spherical origin for reference beams. According to another aspect, the apparatus may include an aperture in a reconstruction arm of the apparatus for aperture selectivity. According to another aspect, the holographic medium may include reflective media.
The present invention enables simplified multiplexing methods and corresponding mechanical systems for holographic reading and recording. Large-scale motions of heavyweight system elements (e.g., holographic medium) can be combined with fine-scale motions of lightweight system elements (e.g., a lens in a reference-beam source) in order to record or read a large number of holograms while avoiding burdensome system requirements.